Annealing method and furnace therefor



July 13, 1937. WILSON ANNEALING METHOD AND FURNACE THEREFOR 2Sheets-Sheet 1 2 Sheets-Sheet 2 L. WILSON ANNEALING METHOD AND FURNACETHEREFOR Filed Feb. 23, 1955 r 1 /n I I Q/ AVr/QAAAAM 9 Jul 13, 1937.

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AM. (0 II Patented July 13, 1937 UNITED STATES ANNEALING METHOD ANDFURNACE THEREFOR v Lee Wilson, Cleveland, Ohio Application February 23,1935, sci-taint. -7,905

6 Claims.

This invention relates to annealing furnaces of the general typedescribed in my U. S. Patent No. 1,952,402 and, specifically, toimprovements in the construction of the furnace disclosed in saidpatent, and a new method of annealing adapted to be practiced with theaid of such improved furnace construction.

In the use of the furnace described in the patent before mentioned; Ihave discovered that the heat exchange tubes or mullies'which con- ;veythe hot gases of combustion along the side walls of the furnacecover,and which are made of heat resistant alloy in order to stand up underthe extreme conditions oftemperature to which they aresubject, exhibit aconsiderabletendency to expand and even to elongate permanently. Ifthese tubes are fixed at both ends, therefore, objectionable stresseswill .be intro 'duced in the operation of the furnace. One object of thepresent invention, therefore, is to provide a furnace in which the heatexchange tubes are fixed at one end only, the other end being permittedto "float, and at the same time, toprovide a gas-tight connectionbetween the 5 floating end and the furnace wall.

Certain difflculties were experienced with the furnace roof,furthermore, because of the passage therethrough of the outlets for thespent heating gases. A further object of the invention, therefore, is toprovide a furnace having outlets forthe spent gases extending outwardlyof the side walls and then upwardly thereof.

It has also been observed that in annealing stacks of-sheets ofdifferent heights, the rates. at which the temperatures of the various"portions of the stack rise are not entirely uniform. Another object ofthis invention, therefore, is to provide a method and means wherebyuniform heating of stacks of various heights may be obtained. In thisconnection, I also provide a method and means whereby the desireduniformity of heating along the length of the stack may likewise beobtained.

Other objects and advantages of the invention will be pointed out in thefollowing detailed description and the novel features ,thereof will bespecifically set forth in the appended claims. for a completeunderstanding of the invention, in connection with the accompanyingdrawings illustrating a present preferred embodiment. In the drawingsFigure 1 is a view partly in plan with a portion thereof shown inhorizontal section, cer-, tain parts being omitted for clearness;

Reference is made to said description- Figure 2 is a side elevation witha'portion in I vertical section;

Figure 3 isa transverse sectional view taken along the line IIIIII ofFigure 1; and

Figure 4 is an end elevation, Referring now in detail to the drawings,the furnace of my invention comprises a base Ill and a cover II. Thebase includes a structural frame I2 having a refractory hearth-I3supported thereon. A sheet metal channel. I 4 extends around the edge ofthe hearth and is adapted to receive a depending flange I5 carried onthe lower edges of the side walls of the cover I l, to provide a fluidseal by virtue of sealing fluid contained in the channel I4. The sidewalls of the cover II, indicated at I6, are composed of refractorymaterial assembled within a structural frame IT. A roof [8' is formed by"a refractory arch sprung from the side walls I6, and a layer ofinsulating material I9 is superposed on the arch. End walls20 similar incharacter to the side walls I6 complete the enclosure provided by thecover II in cooperation with the base I 0. The hearth I3 carries a flatsupporting plate 2|, conveniently a steel plate, which is adaptedto-re'ceive the charge of material to betreated, indicated as a stack 22of ,steel sheets. The cover ll, of course, is'lifted from the base I0while the furnace is being charged. An inner cover 23 is first disposedover the charge. The lower edges of the cover cooperate with a grooveor-recess 23a formed in the hearth I3 and adapted to be filled withsand, whereby to seal the interior ofthe' inner cover from the space outside it. The cover 23 comprises simply an open bottomed metallic shell,the top being formed by a flat plate with suitable bracing membersattached thereto. When the charge 22 and the cover 23 have been placedin position, the cover H is lowered onto the base Ill. This operation isfacilitated by guide pins 23- secured to and extending upwardly from thebase I0 .and guide rings 23" secured to the lower edges of the cover IIand adapted to slide down over the pins 23. 7

Referring again to'the construction of the .cover I l, the side walls I6thereof are provided with a plurality of heat exchange tubes 24. Only afew of these are shown in the drawings, but there isa, continuous seriesof them on both sides of the cover. Although these tubes are shownvertical, they may be disposed in any convenient relation to the axes ofthe cover. The tubes'Zl, are reentrant, having generally a U-shape, the

lower ends being embedded in the refractory forming the side walls. Themiddle portions of the tubes extend upwardly of the side walls I6 andthe upperends extend outwardly thereof through openings 25 which arelarger than the tubes themselves. The tubes are thus fixed'only at theirlower ends, the upper ends being permitted to float so that expansion ofthe tubes on heating, or permanent elongation thereof after considerableuse, will not subject the tubes to any stress. Top lines 25 areconnected to the upper ends ofthe tubes 24 to carry the spent heatinggases upwardly of the furnace.

In order to seal the joints between the upper ends of the tubes 24 andthe opening 25, I provide the lines 26 with L-shaped sleeves 21. Thelower ends of the sleeve extend into the refractory side wall l6 andentirely enclose the outer ends of the holes 25. The upper ends of thesleeves are provided with sealing cups 28 adapted to contain sealingfluid. Sealing bells 29 carried on the flues 26 project dovmwardly intothe cups 28 and the sealing fluid contained therein. Free expansion ofthe tubes 24 and the flues 26 is thus permitted, while the interior ofthe furnace is completelysealed from the atmosphere surrounding it. e

- The tubes 24 are disposed, as stated, along the side walls of thefurnace cover, but preferably not on the ends, and, when combustiongases are passed through the tubes, the furnace charge is heated byconvection and radiation to the anhealing temperature. Currents of hotgases are set up within the cover and these currents generally rise inthe space between the'sides of the cover II and the inner cover 23,sweep over the top of the cover 23 and diverge toward the ends thereoffrom which they descend in the space between the ends of the inner coverand the cover II and then return to the lower portion of the spaceoccupied by the tubes 24. The tubes may,

alternatively, extend inwardly of the end walls and along the. sidewalls, generally horizontally, by merely increasing the length of theelbows thereof to approximately the length of the cover.

Combustion gases for heating the interior of the furnace cover bypassage through the tubes 24 are delivered to the latter by burners 30projecting into the lower ends of the tubes. Air for combustion isdelivered to the burners through manifolds 3|, by manifolds 32 extendingalong the lower edges of the side walls of the cover Individual valves304; control the volume of air delivered to the burners from themanifolds. The lower ends of the tubes 24 are open for the induction ofsecondary air.

The manifolds 3| and 32 extend around one end of the cover as shown inFigure 4, and connect with Ts 33 and 34. The horizontal branchesof theTs are connected to the manifolds by slip joints 35, which permit themanifolds to be moved laterally of the Ts without breaking theconnection therebetween. Fexible hose connections may be used instead ofthe slip joints. The vertical'branch of the T 33 is connected to thedischarge port of a blower 36 mounted on the end of the cover andadapted to be driven by a motor 3|- similarly mounted. -A gate valve 38controls the volumeof air delivered to the manifolds 3| by the blower34. This arrangement is provided for artificial cooling of the furnaceas will be explained later. The T 34 is tapped into the 'T 33 above thevalve 38 for supplying air to the burners during firing. Individualvalves 39 in the horizontal branches of the T 34 permit the distributionof air blast between the two sides of the furnace and, therefore, therates of combustion on such sides, to be varied. The vertical branchoffthe T 34 includes a valve 34a.

The manifolds 3| and 32 are adjustably supported on brackets 40extending outwardly from the side walls of the cover Clamping boltsextend through suitable holes in lugs depending from the manifold andslots in.the brackets, whereby the manifolds 3| and hence the burners30, may be adjusted toward or away from the side walls. l6. Thisadjustment permits the hot spo or zone of maximum temperature of thecombustion gases to be shifted along the tubes 24. With the burners intheir extreme in position, the point of maximum combustion rate isobviously farther up the tubes 24 than when the burners are in theirextreme outposition.. Be-

tween these two extremes, considerable latitude is afforded for placingthe hot spot at the proper level, depending on the height of the stack22, to supply the heat absorbedby the base plate and to insure that allportions along the height of the stack will have their temperatureincreased at substantially the samerate, whereby uniformity of heatingand annealing is obtained.

The fuel supply for the burners 3|) includes gas manifolds 4| havingindividual valved connections 42 to the burners 30. The manifolds 4| aresuspended on the manifolds 3| by these connections and move therewith.The manifolds 4| are connected to a T 43 through slip joints 44 andregulators 45, the latter serving. to maintain a constant pressure inthe manifolds. The slip connections, of course, permit lateraladjustment of the manifolds. The T 43 is connected to a source ofgaseous fuel by any convenient means such as a flexible hose line.Although the furnace disclosed herein is shown as adapted for gaseousfuel, the construction may be modified to burn other types of fuel suchas liquid fuel.

By manipulating the valves controlling the supply of fuel to theindividual burners, it is possible to vary the rate of combustion alongthe length of the side walls of the furnace. Considerable heat isabsorbed by the ends of the sheets in the stack from the gaseouscurrents descending thereover as above explained, and I therefore preferto adjust the fuel valves of the burners adja'cent the ends of the coverto supply less fuel to the burners than supplied by the valves of theburners toward the middle of the side walls. Overheating and welding ofthe sheets adjacent the ends isthus avoided, and uniformity of annealingassured. It is. sometimes desirable to cool the charge after annealingat a rate greater than that caused by natural radiation. To this end,valve 34a is closed and valve 38 opened, reversing their relacover to beobserved when the latter is placed on the hearth or base. Conduits suchas that indicated at 41, permit the introduction of an at- 2,086,970portions of the charge is made possible with a resulting uniformity inthe product, which is greatly to be desired. The proper adjustment ofthe points of maximum temperature may be easily obtained. as regardsboth the height and the length of the charge. The heat exchange tubes ormuflles are mounted with one end floating to prevent stressing thelatter as a result of expansion and contraction,

spirit of the invention or the scope of the follow;

ing claims.

I claim:

1. A furnace comprising a hearth, side and end walls and a roof,manifolds extending along the side walls for supplying an element of combustion toburners spaced along said side walls, a

connection adjacent one of the end walls 'to a source of said element,and extensible joints between said'connections and said manifolds.

2. In a method of heating a furnace chamber to treat a'charge ofmaterial therein, the steps including introducing combustion gases intothe chamber, confining them out of direct contact with said material,-and moving the point of delivery of the gases to vary the location ofthe hottest zone produced thereby.

.3. In a method of annealing in a liftable, openbottomed furnace chamberhaving side and end walls, to treat uniformly a charge of materialtherein, the steps including supplying combustion gases to the chamberat spaced points along the side walls, confining the gases out ofcontact with the material, and supplying a greater quantity of suchgases per unit length of side wall to the middle portion thereof than tothe portions adjacent the end walls.

4. In'a method of annealing in a liftable, openbottomed furnace chamberhaving side and end walls, to treat uniformly a charge of materialtherein,-the steps including supplying combusbut a perfect seal ismaintained at all times to tion gases to the chamber at spaced pointsalong y the side walls, and restricting the supply of such gasesadjacent the end walls.

5. In a method of heating a charge of material 'in a chamber, the stepsincluding introducing combustion gases into the chamber adjacent thebottom of the charge, confining them out of direct contact with saidcharge while conducting them upwardly alongside the charge, and shiftingthe point of delivery of said gases and, therefore, the point of maximumcombustion rate, vertically of the charge to cause uniform heating ofthe material throughout the height of the charge. 1

6. An annealing furnace comprising a base adapted to receive a charge ofmaterial, a cover adapted to be positioned on the base to enclose thecharge, heat-exchange tubes extending through the side wall of the coveradjacent the base, upwardly along the side wall, and outward--

